This application claims the priority of German patent document 10 2005 062 030.2-13, filed Dec. 22, 2005, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a heat shield for mounting on a heat-radiating object, particularly on a rocket engine.
To protect rocket engines from heating up as a result of intensive heat radiation of the engine nozzles, it is known to arrange heat shields between the thrust chamber of the engine and the nozzle expansion. A heat shield according to the state of the art consists of a dish-shaped metal plate whose shape essentially represents a cut-off flat cone. The metal plate therefore forms a conical ring which is mounted between the nozzle expansion and the remaining engine. The metal plate partially deflects the thermal radiation of the hot nozzle by reflection on its front side. This solution has the disadvantage that only a limited fraction of the heat flow can be reflected directly by emissivity of the metal surface of the heat shield. The remaining heat flow is emitted by the back side of the metal plate toward the remaining engine, and heats the latter to an extent that exceeds the demanded low temperatures of newly developed engines.
It is therefore an object of the invention to create a heat shield for mounting on a heat-radiating object, which ensures a still more effective heat shielding of the radiative heat flow generated by the heat-radiating object.
This and other objects and advantages are achieved by the heat shield according to the invention, which comprises a first planar element having a front side and a back side. In the mounted condition of the heat shield on the heat-radiating object, the first planar element extends from the heat-radiating object toward the outside, and its front side is exposed to the heat radiation at least of a section of the heat-radiating object. Furthermore, a second insulating planar element having a front side and a back side is provided in the heat shield according to the invention, arranged on the back side of the first planar element, such that a gap is formed between the back side of the first planar element and the front side of the second planar element. In the mounted condition of the heat shield, the gap widens in the direction from the heat-radiating object toward the outside.
By using a second insulating planar element and an expanding gap, a clearly enhanced reduction of the back-side surface temperature of the heat shield is achieved in comparison to known heat shields. In particular, the heat radiation emitted by the first planar element by way of its back side is, for the most part, radiated to the outside by reflections in the expanding gap in the direction away from the heat-conducting object. The still remaining heat radiation is insulated by the additional second insulating layer, so that only a very small fraction of the heat generated by the heat-radiating object reaches the back side of the heat shield.
In a preferred embodiment of the heat shield according to the invention, the first planar element comprises, at least in part, a metallic material. Metallic materials have a low emissivity, so that a large portion of the heat radiation is already reflected by the front of the first planar element, without arriving in the gap. As a result, a particularly good heat shield is obtained. To reduce the emissivity further, the front and/or back side of the first planar element preferably has a chemically inert coating. This coating, such as for example, gold, particularly an electroplated gold coating.
Particularly when the heat shield is used in a rocket engine, an essentially ring-shaped disk is used as a first planar element, which is arranged, for example, around the cylindrical engine body of the rocket engine and extends from the body essentially perpendicularly to the outside.
In a preferred further embodiment of the invention, the second planar element is insulated by an insulation material, particularly an insulating mat, arranged between the front and the back of the second planar element.
In order to achieve particularly a low emissivity of the front of the second planar element, both the front and, as required, also the back, of the second planar element is made at least partially of a metallic material. As a result, a very good dissipation of the radiative heat flow within the gap toward the outside away from the heat-radiating object is achieved.
Analogous to the first planar element, the front and/or back side of the second planar element preferably has a chemically inert coating, which may also be gold, particularly an electroplated gold coating.
According to a feature of the invention, the second planar element essentially may form a ring-shaped section of a cone. Such a shape of the second planar element is advantageous for its production because metal sheets, which can be unrolled, can be used for the front and back side of the planar element during its manufacturing.
In another embodiment of the invention, the gap between the back of the first planar element and the front of the second planar element has an essentially V-shaped cross-section, the point of the V-shape being situated adjacent to the heat-radiating object and adjoining the latter. This configuration effectively prevents heat radiation from exiting the gap in the direction of the heat-radiating object, and ensures a better heat shield.
In another embodiment of the heat shield according to the invention, the gap between the back of the first planar element and the front of the second planar element in the mounted condition of the heat shield is opened at its end situated away from the heat-radiating object, thereby achieving a very good removal of the heat radiation within the gap away from the heat-radiating object.
In a further embodiment of the invention, one or more holding elements are arranged between the back of the first planar element and the front of the second planar element. These holding elements ensure a secure connection between the partially very thin first planar element and the second planar element.
Preferably the holding elements are fastened to the first and/or second planar element, permitting a thermal expansion of the first and/or second planar element. Because of the considerable expansion of the materials due to the effect of heat, deformations caused by thermal expansion occur at the fastening of the holding elements are prevented. The holding elements are preferably strip-type, particularly sheet metal strips. The weight of the overall construction is thereby reduced.
In a further embodiment of the invention, the heat shield comprises a flange element to which the first and second planar elements are fastened, and which is used for mounting the heat shield on the heat-radiating object. This flange element preferably has an essentially ring-shaped construction, and the first and second planar elements are fastened to the flange element by means of screwed and/or welded and/or riveted connections. In this case, the flange element preferably has a plurality of recesses which separate contact surfaces of the flange element from one another; in the mounted condition of the heat shield, the contact surfaces rest against the heat-radiating object. By the providing of recesses, the contact surface of the flange element is reduced in the direction of the heat-radiating object, whereby an undesirable heat transfer toward the heat-radiating object is avoided. In addition, the recesses in the flange element can be used for the leading-through of electric cables.
For a particularly simple and effective fastening of the heat shield, the latter comprises a plurality of ring-shaped segments of a circle (particularly 120° segments), which can be mutually connected to form a closed ring during mounting on the heat-radiating object.
In another embodiment of the invention, another planar element is arranged on the back of the second planar element in such a manner that another gap, particularly in a V-shape, is formed between the back of the second planar element and the additional planar element. The temperature of the back of the second planar element can be reduced again by removal of heat radiation via the gap.
In addition to the above-described heat shield, the invention also relates to a rocket engine, comprising a thrust chamber for the propellant combustion and a nozzle expansion for the exiting of propellant. The heat shield according to the invention is arranged between the thrust chamber and nozzle expansion such that the front of the first planar element adjoins the nozzle expansion. In this manner, heat radiation from the intensively heating-up nozzle expansion in a racket engine can be effectively prevented from reaches the thrust chamber which is to be protected from heat.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.